Cycles: prevent part of texture from being illuminated (AO, no shine, etc)
Ok, so I actually did this before but forgot, and since I don't see this solution anywhere else (until mods come and point it out to me), here is the solution:
Specular.
Create an AO map where the baseline color is &quot;50% gray&quot; (HSV: 0,0,0.5) and the completely occluded areas are 100% black (HSV: 0,0,0). (I make all my grayscale maps &quot;grayscale&quot; color mode but am always disappointed by how little effect that has on file size.) Plug that into the Specular property of your Principled BSDF shader.
Before:

After:

In case that is too subtle...
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After: